This invention relates to an injection stretch blow molding apparatus and method wherein containers are stretch blow molded from preforms retaining heat from when they were injection molded. This invention also relates to an injection stretch blow molding apparatus and method wherein N (N.gtoreq.2) preforms are simultaneously injection molded and n (1.ltoreq.n&lt;N) preforms among these are simultaneously blow molded into n containers. More particularly, the invention relates to an injection stretch blow molding apparatus and method with which while ample cooling time is provided the preforms can be molded with a shortened injection molding cycle time and furthermore the operation rate of the blow cavities can be increased. Also, this invention relates to constructions and methods for heating and adjusting the temperature of the preforms before they are blow molded. Also, this invention relates to an injection stretch blow molding apparatus and method with which it is possible when necessary to discharge the preforms to outside the apparatus instead of carrying them to the blow molding section.
Methods for blow molding a container from a preform (parison) include that known as the cold parison or 2-stage method and that which is known as the hot parison or 1-stage method. In both these methods, for injection molding the preforms required for the blow molding, at least an injection cavity mold which shapes the outer wall of the preform and an injection core mold which shapes the inner wall of the preform are necessary. Also, after the injection cavity mold and the injection core mold are clamped together and the preform is injection molded, with the molds still clamped together it is necessary to cool the preform down to a temperature at which the preform can be released from the molds.
Particularly in the case of the cold parison (2-stage) method, because this preform mold-release temperature has to be made quite low, the injection molding cycle time has been long and productivity has been poor. This is because when the preform is ejected by the injection cavity mold and the injection core mold being released from the preform and the preform being dropped or the like, it is necessary for the preform to be cooled to a mold-release temperature low enough for the preform not to be deformed when it makes contact with other members.
In the case of the cold parison method, because the preform molding step and the step in which a container is blow molded from this preform are completely release, the blow molding cycle time is not affected by the injection molding cycle time. However, because the cold parison method involves reheating preforms which have been cooled to room temperature the cold parison method is inferior to the hot parison method in its energy efficiency.
In a hot parison (1-stage) method injection stretch blow molding machine which draw blow molds bottles from preforms still containing heat from when they were injection molded the cycle time of the overall apparatus is determined by the injection molding cycle time, which of all the cycles is the one requiring the most time. Consequently there has been the problem that when the time required for injection molding is long, the throughput of the whole apparatus is low.
In the case of the hot parison method, although the preform is mold-released at a higher temperature than in the cold parison method, there is a limit on this mold-release temperature and consequently it is not possible to greatly speed up the injection molding cycle. One reason for this is that when the preform mold-release temperature is high, when the injection core mold is released from the preform, a mold-release called lifting, wherein the preform sticks to the core mold, occurs. Also, after the injection core mold is released from the preform, because there is no longer any member restricting deformation of the preform, deformation caused by temperature nonuniformity and thermal contraction and the like make it impossible for preforms conforming to the design to be ejected. Furthermore, when the cooling effected by the injection core mold is inadequate, crystallization caused by inadequate cooling occurs, particularly at the inner wall of the preform, and a preform of which the trunk portion is opaque is ejected.
Also, when preforms are ejected before they are completely cooled by the injection core mold and the injection cavity mold (with the preforms still at a temperature at which blow molding is possible) and blow molding is carried out thereafter, there have been the following problems:
(A) Unless the internal pressure (injection sustain pressure) is raised, shrink marks form at the injection cavity mold side of the preform and a preform with a uniform temperature distribution cannot be obtained. Consequently, when this preform is blow molded, a molded product with a uniform wall thickness distribution cannot be obtained.
(B) When the internal pressure (injection sustain pressure) is raised, a pressure differential forms between the gate portion and the preform end portion (for example the neck portion), and the resulting preform has large residual stresses at the preform bottom end where the pressure was high. Consequently, when the preform is blow molded, a molded product with a uniform wall thickness distribution cannot be obtained.
(C) When the preform is cooled by the injection core mold and the injection cavity mold, as the cooling progresses the preform contracts and tends to move away from the injection cavity surface. Because of this, there are some parts of the outer wall surface of the preform which are in contact with the injection cavity and some parts which are not in contact with the injection cavity, and consequently different parts of the preform cool at different rates and the temperature becomes uneven. As a result, when this preform is blow molded, a molded product of uniform wall thickness cannot be obtained.
Thus, in a conventional hot parison system, unless the preform is amply cooled by the injection cavity mold and the injection core mold it has not been possible to obtain good blowing characteristics or good bottle characteristics. Because of this, the injection molding of the preforms has required time, and the throughput of the apparatus has been low.
Various other problems have also been associated with injection stretch blow molding machines using the hot parison method, including the following:
When in order to increase the throughput the number N of preforms injection molded simultaneously is increased, the same number N of cavities conforming to the external shape of the bottles being manufactured have to be formed in the blow cavity mold. Of the molds used in a blow molding machine the blow cavity mold is the most expensive, and the cost of this blow cavity mold increases roughly in proportion to the number of cavities in it. Even if a mold is expensive, if its operation rate is high then it can be used cost-effectively; however, because as described above the cycle time of the overall apparatus depends on the injection molding cycle time and cannot be shortened, the operation rate of each cavity in the blow cavity mold has unavoidably been low. Also, when the number of bottles blow molded simultaneously increases, not only the number of cavities in the blow mold but also the number of drawing rods and blow core molds and mechanisms for supporting and driving these increases, and this has resulted in increases in the size and cost of the apparatus.
Another problem has been that conventionally it has not been possible to eject the preforms unless the injection core mold is completely pulled out of the preforms, and consequently with a rotary injection molding apparatus it has not been possible to carry the preforms from the injection molding section to the next stage. When on the other hand the injection core mold is completely pulled out of the preforms, there has been the problem that this pullout stroke is long and the overall height of the apparatus is high.
Another problem has been that when hot parison blow molding is carried out by a rotary carrier type blow molding machine the injection molded preforms are always carried by the rotary carrier to the blow molding section. Here, for example when a problem has arisen in the blow molding section, there has been no alternative but to shut down the preform injection molding as well as the blow molding section. However, once the injection molding section is shut down, a long starting-up time is required when it is restarted. This is because the injection apparatus contains numerous resin-heating mechanisms in the hot runner mold and elsewhere.
As a result, as well as it not being possible to raise the throughput of the overall apparatus, as described above, a lot of time is required for starting up the apparatus when a problem has arisen, and the productivity falls even further.
Accordingly, it is an object of the invention to provide an injection stretch blow molding apparatus and method with which while ample preform cooling time is provided the injection molding cycle time can be shortened and the cycle time of the overall apparatus can thereby be shortened.
Another object of the invention is to provide a highly efficient injection stretch blow molding apparatus and method with which while reducing costs by reducing the number of cavities in the blow mold the operation rate of the blow mold can be increased.
Another object of the invention is to provide an injection stretch blow molding apparatus and method which while exploiting the heat energy efficiency of hot parison molding also has the preform temperature distribution stability of the cold parison method.
Another object of the invention is to provide an injection stretch blow molding apparatus and method with which temperature nonuniformity and deformation can be prevented even when the preform mold-release temperature at which the preforms are released from the injection cavity mold is made high and furthermore the preforms can be amply cooled before they are released from the injection core mold and can be stably blow molded thereafter at a suitable blow molding temperature.
A further object of the invention is to provide an injection stretch blow molding apparatus and method with which the temperature difference between the inner and outer walls of the preforms is moderated before the preforms are blow molded.
A further object of the invention is to provide an injection stretch blow molding apparatus with which general-purpose medium-sized containers of capacity 1 to 3 liters can be blow molded with high efficiency.
A further object of the invention is to provide a blow molding apparatus with which it is possible to efficiently heat the regions below the necks of the preforms to a suitable blow molding temperature.
A further object of the invention is to provide a blow molding apparatus with which it is possible to moderate the temperature difference between the inner and outer walls of the preforms and also use this time provided for temperature moderation to adjust the temperature of the preforms to a suitable blow molding temperature before blow molding is carried out.
A further object of the invention is to provide an injection stretch blow molding apparatus and method which can be started up without any wasteful blow molding being carried out at the time of start-up and with which it is not necessary to stop the operation of the whole apparatus when there is a problem in the blow molding section.
An injection stretch blow molding apparatus according to the invention comprises:
a preform molding station for injection molding preforms;
a blow molding station for stretch blow molding the preforms into containers; and
a transfer station for transferring the preforms from the preform molding station to the blow molding station, wherein the preform molding station comprises:
a circulatory carrier for intermittently circulatorily carrying along a carrying path a plurality of injection core molds disposed apart;
an injection molding section for injection molding the preforms having an injection cavity mold together with which the injection core molds, stopped in the carrying path, are severally clamped; and
an ejecting section for ejecting preforms from the injection core molds by releasing the injection core molds, stopped in the carrying path, and the preforms.
An injection stretch blow molding method according to the invention for blow molding containers from preforms retaining heat from when the preforms were injection molded comprises the steps of:
releasing the preforms, molded using at least an injection core mold and an injection cavity mold, from the injection cavity mold;
with the preforms held by the injection core mold, carrying the injection core mold to an ejecting section along a carrying path while the preforms are cooled by the injection core mold;
in the ejecting section, ejecting the preforms by releasing the injection core mold therefrom; and
thereafter, blow molding the containers from the preforms retaining heat from when the preforms were injection molded.
According to these inventions, the preforms injection molded in the injection molding section are cooled by the injection cavity mold and the injection core mold and then the injection cavity mold only is released from the preforms. After that, the preforms are carried to the preform ejecting section by the injection core mold. The preforms are ejected after being cooled by the injection core mold during this carrying and in the preform ejecting section. As a result, by the preforms being cooled by the injection core mold even after the injection cavity mold is mold-released in the injection molding section, ample preform cooling time is provided. Therefore, the preform mold-release temperature at which the preforms are released from the injection cavity mold can be made high, the injection molding cycle time can thereby be shortened and the cycle time of the overall apparatus can be shortened. Also, even when the preforms are released from the injection cavity mold at a high temperature, deformation of the preforms is prevented by the injection core mold. Furthermore, not only does the cooling efficiency increase because the preforms contract into contact with the injection core mold as they are cooled, and consequently crystallization and loss of transparency of the trunk portions of the preforms caused by inadequate cooling is prevented, but also by thus stabilizing the cooling process it is possible to stabilize the amount of heat retained by the preforms and thereby stabilize the wall thickness distributions of successively blow molded containers.
According to another aspect of the invention, an injection stretch blow molding apparatus comprises:
a preform molding station for injection molding preforms;
a blow molding station for stretch blow molding the preforms into containers; and
a transfer station for transferring the preforms from the preform molding station to the blow molding station,
wherein the preform molding station comprises:
a first circulatory carrier for intermittently circulatorily carrying along a first carrying path an injection core mold having N(N.gtoreq.2) of core pins disposed apart;
an injection molding section for simultaneously injection molding N of the preforms, said injection molding section having an injection cavity mold including N of cavities in which the injection cavity mold is clamped together with the injection core mold stopped in the first carrying path; and
an ejecting section for ejecting preforms from the injection core mold by releasing from the injection core mold, stopped in the first carrying path,
and the blow molding station comprises:
a second circulatory carrier for intermittently circulatorily carrying along a second carrying path the preforms transferred from the preform molding station by the transfer station; and
a blow molding section for simultaneously blow molding n (1.ltoreq.n&lt;N) of containers from n of the preforms, said blow molding section having a blow mold including n of blow cavities in which the blow mold is clamped around the preforms stopped in the second carrying path.
According to another aspect of the invention, an injection stretch blow molding method for molding containers from preforms retaining heat from when the preforms were injection molded, comprising the steps of:
releasing N (N.gtoreq.2) of the preforms, molded using at least an injection core mold and an injection cavity mold, from the injection cavity mold;
with the preforms held by the injection core mold, carrying the injection core mold to an ejecting section along a first circulatory carrying path while the preforms are cooled by the injection core mold;
in the ejecting section, ejecting the preforms by releasing from the injection core mold;
transferring the ejected preforms to carrier members to be carried along a second circulatory carrying path;
carrying the carrier members supporting the preforms along the second carrying path to a blow molding section; and
in the blow molding section, simultaneously blow molding n (1.ltoreq.n&lt;N) of containers from n of the preforms in a blow mold clamped around n of the preforms.
According to these inventions, the inventions provide the following operations and effects in addition to those of the inventions as described above: Because the number n of preforms simultaneously blow molded is made smaller than the number N of preforms simultaneously injection molded, fewer cavities are required in the blow mold and mold costs, molds being consumable items, can be greatly reduced. Also, because fewer blow core molds, stretching rods, and mechanisms for supporting and driving these are required, the apparatus can be made more compact and cheaper. Furthermore, because N simultaneously molded preforms are blow molded n (n.ltoreq.N) at a time over a plurality of blow molding cycles within the shortened injection molding cycle time, the operating rate of the n cavities in the blow cavity mold increases.
Here, a heating section for heating the preforms being carried to the blow molding section can be provided. When this is done, the preforms can be brought to a temperature suitable for blow molding by cooling performed by the injection molds and reheating of the cooled preforms, and the temperature stability from cycle to cycle therefore increases. Also, even though N simultaneously injection molded preforms are blow molded n preforms at a time over (N/n) blow molding cycles, control reducing the temperature variation among blow molding cycles can easily be carried out.
Also, when the preforms being heated are rotated about their vertical center axes, heating unevenness is reduced and temperature nonuniformity in the circumferential direction of the preforms can thereby be reduced.
Furthermore, a second circulatory carrier comprises a plurality of carrier members which remain spaced at equal intervals along the second carrying path, and each of the carrier members has a supporting portion for supporting a preform in an inverted or an upright state. It is preferable that the array pitch at which the plurality of carrier members are spaced along the second carrier path be made equal to the array pitch P of the plurality of cavities in the blow cavity mold. This is because it makes pitch conversion in the carrying process unnecessary. When this is done, the array pitch of the preforms in the heating section of the invention is greater than the small pitch at which the preforms are arrayed in the heating section in a conventional 2-stage system. However, because in this invention it is only necessary to give the preforms a small amount of heat energy in addition to the heat which they retain from when they were injection molded, the heating time can be short and the length of the heating section does not have to be made long as it does in the cold parison case.
Also, in the method of this invention, a step of allowing the preforms to cool between the separation of the preforms from the injection core mold and the start of the blow molding step, over a period of time long enough for the temperature difference between the inner and outer walls of the preforms to be moderated, can be provided. Here, when the method of this invention is applied, because the period of time for which the preforms are cooled by the injection core mold in contact with their inner walls is made longer than conventionally, a relatively steep temperature gradient forms between the inner and outer walls of the preforms, and the temperature in the outer wall vicinity becomes greater than that in the inner wall vicinity. By providing this cooling step, this temperature gradient can be moderated and the inner and outer walls of the preforms can be brought to a temperature suitable for blow molding.
Also, in the method of this invention, it is preferable that in the blow molding step n (n.gtoreq.2) containers simultaneously be blow molded from n preforms using n blow cavities arrayed at a blow molding pitch P, that the preforms being carried along the second carrying path be carried with the array pitch of the carrier members kept equal to this pitch P, and that in the preform transferring step a process wherein n preforms are simultaneously transferred to n carrier members is repeated a plurality of times.
When this is done, as well as no carrying pitch conversion in the second carrying path being necessary, even if the number of preforms simultaneously injection molded N is increased, because only n preforms are transferred at a time, fewer than when N preforms are simultaneously transferred, the preforms can be easily correctly positioned on the carrier members, and also no complex mechanisms are required to do this.
According to another aspect of the invention, an injection stretch blow molding method wherein injection molded preforms are transferred from a preform molding station to a blow molding station by way of a transfer station and the preforms are blow molded into containers in the blow molding station is characterized in that:
in the preform molding station the preforms are injection molded in an upright state with open neck portions thereof facing upward;
the transfer station turns the upright preforms upside-down and transfers the preforms to the blow molding station in an inverted state; and
the blow molding station blow molds containers from the inverted preforms.
According to the invention, the preforms are molded in an upright state with their neck portions facing upward. As a result, the injection mold clamping is vertical clamping and is therefore space-saving. Also, because resin is normally injected from the preform bottom portion side, a stable arrangement wherein the injecting apparatus and the injection cavity mold are disposed on a machine bed and the injection core mold is disposed thereabove can be employed. Also, because when the preforms are carried to the blow molding station they are in an inverted state, the openings at their neck portions can be used to have the preforms support themselves easily. Furthermore, because the drawing rods and blow core molds consequently have to be positioned underneath the preforms, they can be disposed using a space in the machine bed and the overall height of the blow molding section can be made low.
According to another aspect of the invention, an injection stretch blow molding method comprises the steps of:
simultaneously injection molding N of preforms made of polyethylene terephthalate using at least an injection core mold and an injection cavity mold;
releasing the preforms from the injection cavity mold;
carrying the preforms to an ejecting section while cooling the preforms by means of the injection core mold;
in the ejecting section, after the preforms have been cooled to a predetermined temperature, ejecting the preforms from the injection core mold;
heating the ejected preforms to a predetermined temperature; and
thereafter, simultaneously blow molding n of containers from n of the preforms,
wherein the ratio of the numbers N and n is N:n=3:1.
According to experiments carried out by the present inventors, in the case of a general-purpose medium-sized container of capacity 1 to 3 liters having a relatively small mouth (the diameter of the opening in the neck portion 2 being about 28 to 38 mm) for which the market demand is large, the ratio of the simultaneous molding numbers N, n should ideally be set to N:n=3:1. That is, it has been found that in the case of this invention wherein the preforms continue to be cooled by the injection core mold even after the preforms are removed from the injection cavity mold and then blow molded thereafter, the time required for the injection molding of a preform for a general-purpose medium-sized container is shortened to approximately 3/4 of that in the case of a conventional injection stretch blow molding apparatus, and an injection molding cycle time of approximately 10 to 15 seconds is sufficient. A blow molding cycle time, on the other hand, of 3.6 to 4.0 seconds is sufficient. Therefore, if this injection molding cycle time is T1 and the blow molding cycle time is T2, the ratio T1:T2 is roughly 3:1, and to mold general-purpose medium-sized containers efficiently the simultaneous molding numbers N, n should ideally be set according to this ratio.
According to another aspect of the invention, an injection stretch blow molding method comprises the steps of:
simultaneously injection molding N (N.gtoreq.2) of preforms; and
simultaneously blow molding n (1.ltoreq.n&lt;N) of containers from n of the preforms retaining heat from when the preforms were injection molded,
wherein N/n is an integer when the injection and blow molding steps are repeated.
When N/n is an integer, for example the N preforms simultaneously injection molded in a first cycle are all used over an integral number (N/n) of blow molding cycles n at a time, and none of these preforms are mixed with and simultaneously blow molded with any of the N preforms simultaneously molded in the subsequent second cycle. If preforms from different injection molding cycles are mixed and blow molded together, the carrying sequence is different from the case wherein preforms molded in the same injection molding cycle are simultaneously blow molded together, and the control and structure of the apparatus become complicated; however, this invention eliminates this problem.
According to another aspect of the invention, a blow molding apparatus wherein preforms carried in an inverted state with neck portions thereof facing downward or in an upright state with the neck portions facing upward are heated in a heating section before being carried to a blow molding section is characterized in that:
the heating section comprises:
a plurality of first heaters disposed at one side of a preform carrying path, spaced apart in a vertical direction and extending in a preform carrying direction;
a reflecting plate disposed facing the first heaters across the preform carrying path; and
a plurality of second heaters extending in the preform carrying direction on both sides of the preform carrying path,
wherein the second heaters are positioned at such a height in the vertical direction that they face regions subject to blow molding in the vicinities of the neck portions of the preforms.
According to the invention, although the region below the neck portion when the preform is upright is the nearest to the cavity surface of the blow cavity mold, it is a region which is to be draw orientated relatively much. By heating this region with the second heaters on either side of the preform, it can be heated to a higher temperature than the trunk portion region heated by the first heaters disposed on one side only, and a high drawing orientation degree can be secured. Also, because the first heaters are disposed on one side only, the arrangement is saving. Furthermore, because the efficiency with which the region below the neck is heated increases, there is the benefit that the heating time can be shortened and the overall length of the heating section can be made short.
According to another aspect of the invention, a blow molding apparatus comprises:
carrier members which support and intermittently circulatorily carry preforms;
a heating section having heaters extending in a preform carrying direction;
an endless carrying member running along the preform carrying direction at least through a heating zone of the heating section; and
a driver for driving the endless carrying member in a forward direction,
wherein each of the carrier members has a rotary driven member for meshing with the endless carrying member and a preform supporting portion which rotates integrally with the rotary driven member, and
the forward direction of the endless carrying member where it meshes with the rotary driven members is opposite to the preform carrying direction.
According to the invention, while the preforms are stopped the preforms are rotated in one direction by the meshing of the endless carrying member moving forward in a fixed direction and the rotary driven member rotated in a fixed position, and temperature nonuniformity of the preforms can thereby be prevented. Also, when the preforms are moving, because the endless carrying member moves forward in the opposite direction to that in which the preforms are being carried, the preforms are rotated faster in the same direction and temperature nonuniformity is similarly prevented. If the endless carrying member were to move forward along with the preforms in the same direction as the rotary driven member, because the preforms would only be rotated by the speed differential between the endless carrying member and the rotary driven member, the preforms would rotate slowly or not at all. Also, there would be cases wherein the direction of the rotation of the preforms was different from that as of when the preforms were stopped. All these situations would cause temperature nonuniformity in the preforms; however, according to the invention, this temperature nonuniformity is eliminated.
According to another aspect of the invention, a blow molding apparatus wherein preforms are intermittently carried to a blow molding section via a heating section is characterized in that:
the heating section comprises a heater extending in a preform carrying direction at one side of a preform carrying path, and
in the carrying path between the heating section and the blow molding section a standby section is provided where at least enough number of preforms for one blow molding cycle are stopped and made to standby before being carried into the blow molding section.
According to the invention, by a standby section being provided before the blow molding section, the temperature distributions in the synthetic resin preforms, which have poor thermal conductivity, can be moderated. Normally, because heating in the heating section is carried out from around the preforms, the inner wall temperature of the preforms becomes lower than the outer wall temperature. By having at least the number of preforms simultaneously blow molded standby after being heated in order to moderate the resulting temperature gradients therein, the blow molding characteristics are stabilized.
Also, by actively carrying out temperature adjustment on the preforms during this temperature moderation time in the standby section, the preforms can be given a temperature distribution for blow molding which could not be obtained just by simply heating the preforms while rotating them.
According to another aspect of the invention, an injection stretch blow molding apparatus comprising a preform molding section for molding preforms and a blow molding section for blow molding containers from the preforms retaining heat from when the preforms were injection molded is characterized in that:
at a location in a path along which the preforms are carried from the preform molding section to the blow molding section there is provided a discharge guide section for guiding preforms which are not to be carried to the blow molding section off the carrying path.
According to another aspect of the invention, an injection stretch blow molding method wherein preforms are injection molded in a preform molding section and these preforms are carried to a blow molding section and containers are blow molded from the preforms retaining heat from when the preforms were injection molded comprises the steps of:
switching to either a container molding operating mode or a preform molding operating mode; and
when the preform molding operating mode is switched to, part way along the preform carrying path leading to the blow molding section, discharging the preforms being molded in the preform molding section to off the carrying path.
According to these inventions, because it is possible to discharge imperfect preforms molded during molding start-up instead of carrying them to the blow molding section, wasteful blow molding can be avoided. Also, when a problem arises in the blow molding section or when adjustments have to be made thereto, repair or adjustment of the blow molding section is possible without stopping the operation of the preform molding station. Once the preform molding station is shut down, it takes a long time to restore the various heating mechanisms to a state wherein molding is possible; however, with this invention this kind of wasteful starting up time is eliminated.